JP7776381B2 - Surface-coated tool, particularly surface-coated forming tap, and manufacturing method thereof - Google Patents

Description

The present invention relates to surface-coated tools, particularly surface-coated forming taps, and to a method for manufacturing the same.

Rolling tools and cutting tools are known as tools for processing metals and other materials. Rolling is a processing method (also known as "plastic processing") in which a material is shaped by applying strong force to it. Cutting is a processing method in which a material is shaped by cutting it.

When forming a female thread in a workpiece using a rolling tool such as a forming tap, the helical formed forming portion of the forming tap (also called the "thread portion") is generally rotated relative to the workpiece, which has already had a pilot hole drilled into it with a drill or other tool, gradually driving the tap into the pilot hole in the workpiece and plastically deforming the pilot hole portion.

However, when the threads of the threading tap begin to plastically deform the pilot hole in the workpiece, deformation resistance occurs, which applies high pressure to the crest portion (also referred to as the "outer diameter") and flank surfaces of the threads of the threading tap. As a result, heat is generated due to intense friction between the threading tap and the workpiece, and heat is generated due to plastic deformation of the workpiece, which can cause the threading tap and the workpiece to become very hot. Meanwhile, the surface of the pilot hole in the workpiece is pressed hard by the threads of the threading tap, causing the metal structure to stretch and peel off. The peeled metal structure can then adhere to the outer diameter and flank surfaces of the threads of the threading tap due to the high pressure at the contact surface with the threading tap and the high temperatures of the threading tap and the workpiece.

To prevent problems like those mentioned above, forming taps are surface treated with a hard coating to give them wear resistance and adhesion resistance (i.e., a smoother surface).

In recent years, numerous developments have been made in the surface treatment of rolling or cutting tools.

For example, Patent Document 1 discloses a hard-coated tool whose surface is coated with a hard coating. More specifically, the tool in Patent Document 1 has an I layer made of a nitride or carbonitride of AlaTibCrCrc (where a, b, and c are atomic ratios, 0.3≦a≦0.7, 0≦b≦0.5, 0≦c≦0.7, and a+b+c=1), and a II layer, which is a composite film made of CrAlN and a BN phase mixed three-dimensionally. The I layer is provided on the surface of the tool base material, and the I layer and the II layer are alternately stacked in four or more layers to form the hard coating. The thickness of the I layer provided on the surface of the tool base material is in the range of 10 nm to 500 nm, while the thicknesses of the other I and II layers are all in the range of 1 nm to 50 nm, and the total thickness of the entire coating is in the range of 0.1 μm to 20 μm.

Patent Document 2 also discloses a cutting tool including a body and a multilayer coating applied to the body. More specifically, the tool of Patent Document 2 has a first layer A of a hard material selected from titanium aluminum nitride (TiAlN), titanium aluminum silicon nitride (TiAlSiN), chromium nitride (CrN), aluminum chromium nitride (AlCrN), aluminum chromium silicon nitride (AlCrSiN), and zirconium nitride ( _ZrN ) applied to the body, and a second layer B of silicon nitride ( _Si3N4 ) applied directly on the first layer A.

Furthermore, Patent Document 3 discloses a surface-coated tool that exhibits excellent adhesion between the substrate and coating and can withstand severe cutting conditions. More specifically, the tool in Patent Document 3 comprises a substrate and a coating formed on the substrate. The substrate includes WC grains and a binder phase containing Co that bonds the WC grains together. The coating includes an adhesion layer in contact with the substrate and an upper layer formed on the adhesion layer. The adhesion layer has a thickness of 0.5 nm to 20 nm. The adhesion layer contains carbides, nitrides, or carbonitrides that include one or more elements selected from Cr, Ti, Zr, and Nb, one or more elements selected from the elements that make up the substrate, and one or more elements selected from the elements that make up the upper layer.

JP 2013-052478 A International Publication No. 2012/016954 Japanese Patent Application Laid-Open No. 2019-069514

Methods such as sputtering and arc ion plating are used to form coatings on tools such as those mentioned above.

Coatings formed by sputtering are known to produce a smooth surface, but compared to coatings formed by arc ion plating, they have a lower ionization rate and therefore a lower density. For this reason, when using coatings formed by sputtering as a surface treatment, there is a problem of insufficient wear resistance, particularly for rolling tools such as forming taps, which are known to be subject to high processing loads.

On the other hand, while the coating formed by the arc ion plating method has a high ionization rate, it is prone to producing molten particles (also called "droplets") measuring submicrons to several microns in size. For this reason, when using a coating formed by the arc ion plating method as a surface treatment, it is difficult to obtain a smooth surface, meaning that the coating cannot achieve sufficient adhesion resistance.

The present invention aims to improve the above situation, and its purpose is to provide a surface-coated tool, particularly a surface-coated forming tap, that has excellent wear resistance and adhesion resistance, and a method for manufacturing the same.

The present invention, which achieves the above objectives, is as follows:

<Aspect 1>
A method for manufacturing a surface-coated tool, comprising the steps of:
the tool includes a substrate and a layer I and a layer II coated in this order on a surface of the substrate;
the layer I and the layer II are each independently at least one of a titanium nitride coating, a titanium carbide coating, and a titanium carbonitride coating; and the method includes the following steps (1) to (3):
(1) forming the layer I on the substrate by an arc ion plating method;
(2) subjecting the layer I to an ion bombardment treatment using metal ions; and (3) forming a layer II by a sputtering method on the layer I after the ion bombardment treatment.
<Aspect 2>
The method according to aspect 1, wherein a relationship between an arithmetic mean roughness Ra ₀ of the surface of the base material and an arithmetic mean roughness Ra ₂ of the surface of the II layer satisfies the following formula (1):
0μm≦Ra ₂ −Ra ₀ <0.060μm (1)
<Aspect 3>
3. The method according to claim 1, wherein the arithmetic mean roughness Ra of the surface of the layer II is 0.150 μm or less.
<Aspect 4>
Aspect 4. The method according to any one of Aspects 1 to 3, wherein in step (2), the metal ion is a Cr ion.
Aspect 5
Aspect 5. The method of any one of aspects 1 to 4, wherein the tool is a forming tap.
Aspect 6
A substrate, and a layer I and a layer II coated in this order on a surface of the substrate,
the I layer is an arc ion plating layer,
the second layer is a sputtering layer,
the layer I and the layer II are each independently at least one of a titanium nitride coating, a titanium carbide coating, and a titanium carbonitride coating, and the relationship between the arithmetic mean roughness Ra ₀ of the surface of the base material and the arithmetic mean roughness Ra ₂ of the surface of the layer II satisfies the following formula (1):
Surface coated tools:
0μm≦Ra ₂ −Ra ₀ <0.060μm (1)
Aspect 7
A tool according to aspect 6, wherein the arithmetic mean roughness Ra of the surface of the II layer is 0.150 μm or less.
<Aspect 8>
the thickness of the layer I is 1.0 μm or more and 5.0 μm or less, and the thickness of the layer II is 1.0 μm or less;
8. The tool of claim 6 or 7.
<Aspect 9>
A tool according to any one of aspects 6 to 8, wherein the surface of the II layer has a maximum height roughness Rz of 1.300 μm or less.
Aspect 10
Aspect 10. The tool of any one of aspects 6-9, wherein the Layer I is comprised of two or more coatings.
<Aspect 11>
11. The tool of any one of aspects 6 to 10, wherein a surface of the layer I has a Cr content less than 1.0 at.%.
<Aspect 12>
The tool according to any one of claims 6 to 11, wherein the tool is a forming tap.

The present invention makes it possible to provide a surface-coated tool with excellent wear resistance and adhesion resistance.

FIG. 1 is a schematic cross-sectional view showing an example of the configuration of a surface-coated tool of the present invention. FIG. 2 is a schematic cross-sectional view showing an example of the configuration of the surface-coated tool of the present invention. FIG. 3 is a flow chart showing an outline of the steps involved in the manufacturing method of the present invention. FIG. 4 is a side perspective view showing a schematic example of a film forming apparatus used in the present invention. FIG. 5 is a schematic cross-sectional view showing the configuration of the test tap and test piece of Example 1. 6(a) is a surface photograph of the test tap of Example 1, FIG. 6(b) is a surface photograph of the test tap of Comparative Example 1, FIG. 6(c) is a surface photograph of the test tap of Comparative Example 2, and FIG. 6(d) is a surface photograph of the test tap of Comparative Example 3. Fig. 7 is a diagram showing the observation results of the indentation site in Example 1. Fig. 7(b) is an enlarged view of the area enclosed by the square frame in Fig. 7(a). Fig. 8 is a diagram showing the observation results of the indentation site of Comparative Example 1. Fig. 8(b) is an enlarged view of the area enclosed by the square frame in Fig. 8(a). FIG. 9 is a diagram showing the observation results of the indentation site of Comparative Example 2. FIG. 10 is a photograph of the test tap of Example 1 after 1,600 holes were drilled. FIG. 11 is a photograph of the test tap of Comparative Example 3 after 1,600 holes were drilled. FIG. 12 is a photograph of the test tap of Example 1 after 880 holes were drilled. FIG. 13 is a photograph of the test tap of Comparative Example 3 after 880 holes were drilled.

Embodiments of the present invention will be described in detail below with reference to the drawings. For ease of explanation, identical or corresponding parts in each drawing will be designated by the same reference numerals, and duplicate explanations will be omitted. Furthermore, the present invention is not limited to the following embodiments, and various modifications can be made within the spirit and scope of the invention.

<Surface-coated tools>
The surface-coated tool of the present invention (hereinafter also simply referred to as "the tool of the present invention") is
A substrate, and a layer I and a layer II coated in this order on a surface of the substrate,
The first layer is an arc ion plating layer,
The layer II is a sputtering layer,
the first layer and the second layer are each independently at least one of a titanium nitride coating, a titanium carbide coating, and a titanium carbonitride coating, and the relationship between the arithmetic mean roughness Ra ₀ of the surface of the substrate and the arithmetic mean roughness Ra ₂ of the surface of the second layer satisfies the following formula (1):
Surface coated tools:
0μm≦Ra ₂ −Ra ₀ <0.060μm (1)

In the present invention, the tool of the present invention may be a rolling tool or a cutting tool, but is preferably a rolling tool, particularly a forming tap.

Figure 1 is a schematic cross-sectional view showing an example of the configuration of a surface-coated tool of the present invention.

The surface-coated tool 100 shown in Fig. 1 includes a substrate 10 and a layer I 11 and a layer II 12 coated in this order on the surface of the substrate 10. Here, the layer I 11 is an arc ion plating layer, and the layer II 12 is a sputtering layer. The layers I 11 and II 12 are each independently at least one of a titanium nitride coating, a titanium carbide coating, and a titanium carbonitride coating, and the relationship between the arithmetic mean roughness Ra ₀ of the surface of the substrate 10 and the arithmetic mean roughness Ra ₂ of the surface of the layer II 12 satisfies the following formula (1):
0μm≦Ra ₂ −Ra ₀ <0.060μm (1)

In the present invention, the term "arc ion plating layer" refers to a layer or coating formed by the arc ion plating method. Furthermore, the term "sputtering layer" refers to a layer or coating formed by the sputtering method.

As mentioned above, coatings formed by sputtering and arc ion plating can be used as surface treatments for rolling or cutting tools, but each method has its advantages and disadvantages. In either case, it is particularly difficult to achieve both the wear resistance and adhesion resistance required for surface treatment of rolling tools.

The inventors therefore attempted to treat the surface of a rolling tool by combining arc ion plating and sputtering. More specifically, they attempted to form a multilayer film by forming a coating on the surface of a thread forming tap using arc ion plating, and then forming another coating using sputtering.

However, it was found that simply combining arc ion plating and sputtering does not result in a surface treatment coating that is both highly resistant to wear and adhesion. More specifically, it was found that the surface of a coating formed by arc ion plating has many protrusions caused by droplets, and if a coating is then formed by sputtering in this state, the protrusions will be transferred as is, resulting in a failure to improve surface roughness and the possibility of the coating peeling off due to poor adhesion. It was also found that cracks will occur starting from the droplets due to the load applied during the rolling process, which can carry away the entire coating formed by sputtering on the surface, leading to peeling.

In response to this, the inventors conducted further research and discovered that by subjecting a coating formed by arc ion plating to ion bombardment treatment using metal ions before forming the coating by sputtering, they were able to obtain a rolling tool with the desired excellent wear resistance and adhesion resistance. Furthermore, surprisingly, they found that even when ion bombardment treatment using commonly used argon (Ar) ions was performed, the desired effects could not be achieved (see Comparative Example 1).

The tool of the present invention, obtained based on this finding, has a smoother surface than conventional coatings. For example, the relationship between the arithmetic mean roughness _Ra of the substrate surface and the arithmetic mean roughness Ra of the Layer _II surface satisfies the above formula (1), and therefore has excellent adhesion resistance. Furthermore, because Layer I is an arc ion-plated layer, the tool of the present invention also has excellent wear resistance. Furthermore, as explained in detail in the section "Method for manufacturing a surface-coated tool" below, a specific ion bombardment treatment is performed on Layer I before forming Layer II, which makes it possible to flatten the surface of Layer I, thereby improving the adhesion between Layer I and Layer II. As a result, it is believed that the tool of the present invention has higher wear resistance.

In other words, the tool of the present invention, particularly the forming tap, has excellent wear resistance and adhesion resistance.

<Base material>
In the tools of the present invention, the substrate may be, for example, but not limited to, high speed tool steel (HSS), alloy tool steel, carbon tool steel, fine grained cemented carbide or ultra fine grained cemented carbide.

In the present invention, the arithmetic mean roughness Ra ₀ of the surface of the substrate is not particularly limited as long as the relationship with the arithmetic mean roughness Ra ₂ of the surface of the layer II described below satisfies the following formula (1):
0μm≦Ra ₂ −Ra ₀ <0.060μm (1)

In formula (1), the value of Ra ₂ -Ra ₀ is less than 0.060 μm, and more specifically, may be, for example, 0.055 μm or less, 0.050 μm or less, 0.045 μm or less, 0.040 μm or less, 0.035 μm or less, 0.030 μm or less, or 0.025 μm or less, or may be 0 or greater.

In the present invention, the arithmetic mean roughness Ra of a layer or coating can be measured at three locations in accordance with JIS B 0601-2001, and the average value can be used as the arithmetic mean roughness Ra.

<Layer I>
In the tool of the present invention, Layer I is an arc ion plating layer. Because Layer I is an arc ion plating layer, it has a high density and can impart wear resistance to the tool of the present invention.

Layer I may be at least one of a titanium nitride coating, a titanium carbide coating, and a titanium carbonitride coating. Furthermore, Layer I may be composed of a single coating, or two or more coatings; however, from the perspective of further improving wear resistance, it is preferable that Layer I be composed of two or more coatings. When Layer I is composed of two or more coatings, each coating may independently be at least one of a titanium nitride coating, a titanium carbide coating, and a titanium carbonitride coating.

For example, Figure 2 is a schematic cross-sectional view showing an example of the configuration of a surface-coated tool of the present invention. The surface-coated tool 200 of the present invention shown in Figure 2 includes a substrate 20 and layers I 21a-21e and layer II 22, which are coated in this order on the surface of the substrate 20. As shown in Figure 2, layer I is composed of two or more coatings 21a, 21b, 21c, 21d, and 21e. Furthermore, in the surface-coated tool 200, the coatings 21a, 21b, 21c, 21d, and 21e constituting layer I may each independently be at least one of a titanium nitride coating, a titanium carbide coating, and a titanium carbonitride coating. More specifically, for example, layer I may have coating 21a which is a titanium nitride coating, and coatings 21b, 21c, 21d, and 21e which are all titanium carbonitride coatings.

While Layer I may further contain elements other than the elements constituting the titanium nitride coating, titanium carbide coating, and titanium carbonitride coating (i.e., N, C, and Ti), it is preferable for it to contain trace amounts or no elements other than N, C, and Ti. For example, as explained in detail in the section "Method for manufacturing a surface-coated tool" below, before forming Layer II, an ion bombardment treatment using metal ions is performed on Layer I, and it is preferable for Layer I to contain trace amounts or no metal ions used in this ion bombardment treatment, such as chromium (Cr) ions. In other words, when measured with an energy dispersive X-ray analyzer (EDS), the Cr content in the surface of Layer I according to the present invention is preferably less than 1.0 at%, 0.9 at% or less, 0.8 at% or less, 0.7 at% or less, 0.6 at% or less, 0.5 at% or less, 0.4 at% or less, 0.3 at% or less, 0.2 at% or less, 0.1 at% or less, or 0 at%.

In the present invention, the thickness of Layer I is not particularly limited, but is preferably 1.0 μm or more and 5.0 μm or less. More specifically, the thickness of Layer I may be, for example, 1.0 μm or more, 1.5 μm or more, 2.0 μm or more, 2.5 μm or more, 3.0 μm or more, 3.5 μm or more, 4.0 μm or more, or 4.5 μm or more, and may be 5.0 μm or less, 4.5 μm or less, 4.0 μm or less, 3.5 μm or less, 3.0 μm or less, 2.5 μm or less, 2.0 μm or less, or 1.5 μm or less. Note that, in the present invention, the thickness of a layer or coating refers to the arithmetic mean thickness. Furthermore, when Layer I is composed of two or more coatings, the total thickness of these two or more coatings is defined as the thickness of Layer I.

<Layer II>
In the tool of the present invention, Layer II is a sputtering layer. Because Layer II is a sputtering layer, it has high smoothness and can impart adhesion resistance to the tool of the present invention.

Layer II may be at least one of a titanium nitride coating, a titanium carbide coating, and a titanium carbonitride coating. Layer II may be composed of a single coating, or two or more coatings. However, from the perspective of further improving wear resistance while maintaining adhesion resistance, it is preferable that Layer II be composed of a single coating. When Layer II is composed of two or more coatings, each coating may independently be at least one of a titanium nitride coating, a titanium carbide coating, and a titanium carbonitride coating.

For example, the surface-coated tool 200 of the present invention shown in Figure 2 includes a substrate 20, and layers I 21a-21e and layer II 22 coated in this order on the surface of the substrate 20. In Figure 2, layer II 22 is composed of a single coating, but it may also be composed of two or more coatings.

In the present invention, the thickness of Layer II is not particularly limited, but is preferably 1.0 μm or less. More specifically, the thickness of Layer II may be, for example, 1.0 μm or less, 0.9 μm or less, 0.8 μm or less, 0.7 μm or less, 0.6 μm or less, or 0.5 μm or less, or may be 0.02 μm or more, 0.05 μm or more, 0.1 μm or more, 0.2 μm or more, or 0.3 μm or more.

In the present invention, the smoother the surface of Layer II, the greater the adhesion resistance effect. Therefore, the arithmetic mean roughness _Ra2 of the surface of Layer II according to the present invention may be, for example, 0.150 μm or less, 0.140 μm or less, 0.130 μm or less, 0.120 μm or less, or 0.115 μm or less. The lower limit of the arithmetic mean roughness Ra of the surface of Layer II is not particularly limited and may be, for example, 0.010 μm or more.

In addition, in the present invention, the maximum height roughness Rz of the surface of Layer II may be 1.300 μm or less, and more specifically, may be, for example, 1.250 μm or less, 1.200 μm or less, 1.150 μm or less, 1.100 μm or less, or 0.950 μm or less, or may be 0.500 μm or more.

In the present invention, the maximum height roughness Rz of a layer or coating can be measured at three locations in accordance with JIS B 0601-2001, and the average value can be used as the maximum height roughness Rz.

Other demographics
The tool of the present invention may further include other layers as desired, as long as the effects of the present invention are not impaired.

Other layers may include, for example, an optional underlayer to improve adhesion between the substrate and Layer I. Furthermore, if Layer I is composed of two or more coatings, functional layers that provide optional functions may be provided among the coatings that make up Layer I.

<<Method for manufacturing surface-coated tools>>
The method for producing a surface-coated tool of the present invention (hereinafter also simply referred to as the "production method of the present invention") comprises the steps of:
The tool includes a substrate and a layer I and a layer II coated in this order on a surface of the substrate;
wherein the first layer and the second layer are each independently at least one of a titanium nitride coating, a titanium carbide coating, and a titanium carbonitride coating; and the method includes the following steps (1) to (3):
(1) forming a first layer on a substrate by an arc ion plating method;
(2) performing an ion bombardment treatment on the layer I using metal ions; and (3) forming the layer II by a sputtering method on the layer I after the ion bombardment treatment.

In the manufacturing method of the present invention, the "tool," "Layer I," and "Layer II" are described in the "Surface-Coated Tool" section above, so an explanation will be omitted here.

Figure 3 is a flowchart showing an outline of the steps involved in the manufacturing method of the present invention.

The manufacturing method of the present invention shown in Figure 3 includes step (1) forming Layer I on a substrate by arc ion plating (S1), step (2) subjecting Layer I to ion bombardment treatment using metal ions (S2), and step (3) forming Layer II on Layer I after ion bombardment treatment by sputtering (S3).

<Film forming equipment>
The film forming apparatus used in the manufacturing method of the present invention is not particularly limited, and one apparatus may be used, or a plurality of apparatuses may be used in combination.

Figure 4 is a side perspective view showing a schematic example of a film formation apparatus used in the present invention. Steps (1) to (3) according to the present invention can be performed in the film formation apparatus 500 shown in Figure 4.

In the film formation apparatus 500 shown in Figure 4, a target (arc target) 502 serving as the metal source for the coating, a metal source target 503 for ion bombardment treatment, a target (sputtering target) 504 serving as the metal source for the coating, and a rotary substrate holder 505 on which substrates 10a and 10b can be placed are installed within a chamber 501. Power supplies are attached to each of the targets 502, 503, and 504, and a bias power supply is attached to the substrate holder 505. Furthermore, the chamber 501 is equipped with a gas inlet 506 for introducing source gas and a gas outlet 507. The pressure in the chamber 501 can be adjusted by sucking gas from the gas outlet 5072 using a vacuum pump (not shown).

<Process (1)>
In step (1), the first layer is formed on the substrate by arc ion plating.

The arc ion plating method is a deposition method in which a substrate and target are placed in a film-forming device, and a high current is applied to the target to create an arc discharge, ionizing the elements that make up the target, which are then deposited on a substrate to which a negative bias voltage is applied.

More specifically, for example, in the film formation apparatus 500 shown in FIG. 4, substrates 10a and 10b are each attached to a rotary substrate holder 505, and a Ti-containing target 502 is used as the target 502, with nitrogen gas and/or acetylene gas used as the source gas. While rotating the substrates 10a and 10b, a high current is applied to the target 502 to generate an arc discharge, ionizing the elements that make up the target. The source gas is introduced from the gas inlet 506, and the target is deposited on the substrates 10a and 10b to which a negative bias voltage is applied, forming a first layer, which is at least one of a titanium nitride coating, a titanium carbide coating, and a titanium carbonitride coating.

In Figure 4, two substrates, 10a and 10b, are provided, but there may be only one, or even three or more. Furthermore, by adjusting the amount of nitrogen gas and/or hydrocarbon gas (e.g., acetylene gas) used as the raw material gas, the desired titanium nitride coating, titanium carbide coating, and titanium carbonitride coating can be formed.

In step (1), the temperature within chamber 501 is not particularly limited and may be adjusted as appropriate within the range of, for example, 400°C to 500°C. The pressure within chamber 501 is not particularly limited and may be adjusted as appropriate. In addition, the voltage and current applied to the target and substrate may be adjusted as appropriate depending on the type or thickness of the desired coating.

<Process (2)>
In step (2), the layer I is subjected to an ion bombardment treatment using metal ions, which removes droplets formed on the surface of the layer I by the arc ion plating method, i.e., flattens the surface of the layer I.

In step (2), the metal ions used in the ion bombardment treatment may be, for example, Cr ions or Ti ions, but are preferably Cr ions.

More specifically, in step (2), for example, an ion bombardment process can be performed on the layer I formed on the substrates 10a and 10b in the film formation apparatus 500 shown in Figure 4 using a target 503 containing Cr while the substrates 10a and 10b are being rotated.

When performing metal ion bombardment, the bias voltage applied to the substrate can be appropriately adjusted, for example, so that the metal elements used in the ion bombardment do not adhere to the substrate or adhere only in trace amounts.

In addition, step (2) may be carried out in a vacuum or high vacuum atmosphere, and an inert gas such as argon gas may be introduced as appropriate.

<Process (3)>
In step (3), the layer II is formed by sputtering on the layer I after the ion bombardment treatment.

Sputtering is a deposition method in which Ar ions generated by glow discharge bombard the surface of a target material, ionizing the atoms emitted from the target and depositing them on a substrate.

More specifically, for example, a target containing Ti is used as the target 504 in the film formation apparatus 500 of FIG. 4, and nitrogen gas and/or acetylene gas is used as the source gas. During this process, while the substrates 10a and 10b are rotated on the layer I after the ion bombardment process, Ar ions generated by glow discharge are bombarded against the surface of the target 504, ionizing the Ti atoms released from the target 504. Furthermore, source gas is introduced as necessary to form layer II, which is at least one of a titanium nitride coating, a titanium carbide coating, and a titanium carbonitride coating.

<Optional Other Steps>
The manufacturing method of the present invention may optionally include other steps in addition to the steps described above, such as, but not limited to, an etching step.

(Etching process)
For example, the manufacturing method of the present invention may further include etching the substrate before step (1). By performing the etching, fine dirt and the like adhering to the surface of the tool of the present invention can be removed.

Etching can be performed using dry etching such as reactive gas etching or reactive ion etching.

The present invention will be described in more detail below using examples, but the present invention is not limited to these examples.

Example 1
In Example 1, a test tap (also referred to as an "evaluation tap") and a test piece for measurement, each having the configuration shown in FIG. 5, were manufactured.

More specifically, high-speed tool steel (HSS) was used as the substrate. Layer I, coated on the surface of the substrate, included multiple TiN and TiCN coatings formed by arc ion plating, with a total thickness of 2.0 μm. Furthermore, the surface of the top layer of Layer I (i.e., the layer adjacent to Layer II) was subjected to Cr ion bombardment treatment, and after this treatment, Layer II was formed by sputtering. The thickness of Layer II was 0.5 μm.

Comparative Example 1
In Comparative Example 1, a test tap and a test piece for measurement were manufactured in the same manner as in Example 1, except that Ar ion bombardment was performed instead of Cr ion bombardment.

Comparative Example 2
In Comparative Example 2, a test tap and a test piece for measurement were produced in the same manner as in Example 1, except that the ion bombardment treatment was not carried out.

Comparative Example 3
In Comparative Example 3, a test tap and a test piece for measurement were manufactured in the same manner as in Example 1, except that a TiN film was formed on the substrate by hollow cathode discharge, and then a TiCN film was formed thereon, and no ion bombardment treatment was performed.

<evaluation>
(Surface roughness measurement)
For the test taps manufactured in the Examples and Comparative Examples and the corresponding test pieces, the arithmetic mean roughness Ra and maximum height roughness Rz of the substrate before coating, and the arithmetic mean roughness Ra and maximum height roughness Rz of the surface of Layer II after coating were determined, and the results are shown in Table 1.

The arithmetic mean roughness Ra was measured at three locations using a roughness measuring device in accordance with JIS B 0601-2001, and the average value was taken as the arithmetic mean roughness Ra. Furthermore, the maximum height roughness Rz was measured at three locations using a roughness measuring device in accordance with JIS B 0601-2001, and the average value was taken as the maximum height roughness Rz.

(Microscopic observation)
The test taps manufactured in the examples and comparative examples were observed using an electron microscope, and the observation results are shown in Figure 6(a) (Example 1), Figure 6(b) (Comparative Example 1), Figure 6(c) (Comparative Example 2), and Figure 6(d) (Comparative Example 3), respectively.

As is clear from Figures 6(a) to 6(d), the test tap of Example 1 had the smoothest surface and the fewest number of droplets.

(Coating adhesion evaluation by indentation in Rockwell hardness test)
An indentation was made with a diamond indenter (cone) using a Rockwell hardness tester on each of the test pieces of Example 1 and Comparative Examples 1 and 2. Thereafter, each indented portion was observed under an electron microscope, and the respective results are shown in Figures 7 to 9.

In addition, each observation result was evaluated based on the adhesion evaluation standard DIN VDI 3198.

Figure 7 shows the results of observing the indentation site of Example 1. Figure 7(b) is an enlarged view of the area enclosed by the square frame in Figure 7(a). As is clear from Figure 7, in the results of Example 1, only very small cracks were observed even when observed under magnification (Figure 7(b)). This also clearly corresponds to the HF1 (pass) rank in the adhesion evaluation standard DIN VDI 3198. In other words, it was found that the coating of the test piece of Example 1 had high adhesion.

Figure 8 shows the results of observing the indentation site in Comparative Example 1. Figure 8(b) is an enlarged view of the area enclosed by the square frame in Figure 8(a). As is clear from Figure 8, small cracks were observed in the results of Comparative Example 1 when observed under magnification (Figure 8(b)). This corresponds to an HF1 (pass) rank in the adhesion evaluation standard DIN VDI 3198, but was found to be slightly inferior to the adhesion in Example 1.

Figure 9 shows the results of observing the indentation site in Comparative Example 2. Note that the contrast of the photograph in Figure 9 has been adjusted for ease of confirmation. As is clear from Figure 9, the results for Comparative Example 2 show that Layer II (i.e., the sputtering layer) had peeled off. This clearly corresponds to a rank of HF6 (fail) in the adhesion evaluation standard DIN VDI 3198.

A Rockwell hardness test was also conducted on the test piece of Comparative Example 3. The observation results (not shown) of the indentation site of Comparative Example 3 were found to correspond to the HF1 (pass) rank of the adhesion evaluation standard DIN VDI 3198.

The rankings of the indentation results for each of the examples and comparative examples, which correspond to the adhesion evaluation standard DIN VDI 3198, are summarized in Table 1 below.

(Vickers hardness test)
The Vickers hardness of each of the test pieces of Example 1 and Comparative Examples 1 to 3 was measured at a test load of 250 mN in accordance with JIS Z 2244. The results are shown in Table 1 below.

As is clear from the results in Table 1, Example 1, which underwent ion bombardment treatment using Cr ions, had the lowest arithmetic mean surface roughness of Layer II, suggesting that it had the highest adhesion resistance.

<Results of application to forming taps (rolling tools) 1>
The wear resistance and adhesion resistance of each test tap of Example 1 and Comparative Example 3 were evaluated. Photographs of the condition of each tap after drilling 1,600 holes are shown in Figure 10 (Example 1) and Figure 11 (Comparative Example 3).

The hole drilling test conditions are as follows:
Tap: Forming tap M4 x 0.7
Work material: S50C (carbon steel)
Pilot hole diameter: 3.7 mm
Tapping speed: 20 m/min
Cutting fluid: Water-soluble cutting fluid emulsion concentration 5%

As is clear from Figures 10 and 11, there was no significant difference in appearance between Example 1 and Comparative Example 3 in Figures 10(a) and 11(a). However, when observing the enlarged views in Figures 10(b) and 11(b), respectively, it was found that areas where the substrate (base material) was exposed and areas of adhesion were visible at the top of the tap in Comparative Example 3. In contrast, there was no exposed substrate in Example 1.

In other words, it was found that Example 1, which was used as a thread forming tap, had superior wear resistance and adhesion resistance compared to Comparative Example 3.

<Results of application to forming taps (rolling tools) 2>
The wear resistance and adhesion resistance of each test tap of Example 1 and Comparative Example 3 were evaluated. Photographs of the state of each tap after drilling 880 holes are shown in Figure 12 (Example 1) and Figure 13 (Comparative Example 3).

The hole drilling test conditions are as follows:
Tap: Forming tap M2 x 0.4
Work material: SUS304 (material prone to adhesion)
Pilot hole diameter: 1.82 mm
Tapping speed: 5 m/min
Cutting fluid: Water-soluble cutting fluid emulsion concentration 5%

As is clear from Figures 12 and 13, there was no significant difference in appearance between Example 1 and Comparative Example 3 in Figures 12(a) and 13(a). However, when observing the enlarged views of Figures 12(b) and 13(b), Comparative Example 3 had exposed areas of the substrate (base material) and adhered areas. In contrast, in Example 1, although adhered areas were visible, they were not as large as in Comparative Example 3. Furthermore, there was no exposed substrate in Example 1.

These results demonstrate that the test tap of Example 1 has superior wear resistance and adhesion resistance compared to Comparative Example 3.

10, 20, 10a, 10b Substrate 11 Layer I 12, 22 Layer II 21a, 21b, 21c, 21d, 21e Coating constituting Layer I 100, 200 Surface-coated tool 500 Film-forming apparatus 501 Chamber 502, 503, 504 Target 505 Substrate holder 506 Gas inlet 507 Gas outlet

Claims (11)

A method for manufacturing a surface-coated tool, comprising the steps of:
the tool includes a substrate and a layer I and a layer II coated in this order on a surface of the substrate;
the layer I and the layer II are each independently at least one of a titanium nitride coating, a titanium carbide coating, and a titanium carbonitride coating; and the method includes the following steps (1) to (3):
(1) forming the layer I on the substrate by an arc ion plating method;
(2) subjecting the layer I to an ion bombardment treatment using metal ions; and (3) forming a layer II on the layer I after the ion bombardment treatment by a sputtering method .
In the step (2), the metal ion is a Cr ion.
method. The method according to claim 1, wherein a relationship between an arithmetic mean roughness Ra ₀ of the surface of the substrate and an arithmetic mean roughness Ra ₂ of the surface of the II layer satisfies the following formula (1):
0μm≦Ra ₂ −Ra ₀ <0.060μm (1) The method of claim 1, wherein the arithmetic mean roughness Ra of the surface of the second layer is 0.150 μm or less. The method according to any one of claims 1 to 3 , wherein the tool is a forming tap. A substrate, and a layer I and a layer II coated in this order on a surface of the substrate,
the I layer is an arc ion plating layer,
the second layer is a sputtering layer,
the surface of the I layer contains less than 1.0 at% Cr;
the layer I and the layer II are each independently at least one of a titanium nitride coating, a titanium carbide coating, and a titanium carbonitride coating, and the relationship between the arithmetic mean roughness Ra ₀ of the surface of the base material and the arithmetic mean roughness Ra ₂ of the surface of the layer II satisfies the following formula (1):
Surface coated tools:
0μm≦Ra ₂ −Ra ₀ <0.060μm (1) In the formula (1), Ra ₂ -Ra ₀ 6. The tool of claim 5, wherein the value of is 0.030 μm or less. The tool according to claim 5 , wherein the arithmetic mean roughness Ra of the surface of the second layer is 0.150 μm or less. the thickness of the layer I is 1.0 μm or more and 5.0 μm or less, and the thickness of the layer II is 1.0 μm or less;
6. The tool of claim 5 . The tool according to claim 5 , wherein the maximum height roughness Rz of the surface of the II layer is 1.300 μm or less. The tool of claim 5 , wherein the Layer I is comprised of two or more coatings. The tool according to any one of claims 5 to 10, wherein the tool is a forming tap.